Angiotensin I converting enzyme (ACE) forms the hormone, angiotensin (ANG) II. The surplus of ANG II has been implicated in the development of diabetic kidney disease. The recently discovered enzyme, called ACE2, has a high catalytic efficiency to degrade ANG II to ANG 1-7. This suggests an important role of ACE2 in preventing ANG II accumulation, and enhancing ANG 1 -7 formation. To the extent that ACE2 plays a significant role in counterbalancing and attenuating ANG II accumulation at the kidney level, one must consider a role of alterations in renal ACE2 in kidney disease. Like ACE, ACE2 is localized within the glomerular tuft area, and therefore may function to limit the amount of ANG II in the glomerulus. In glomeruli from diabetic mice there is a distinctive pattern of ACE2 and ACE expression (low ACE2, but increased ACE). The proposed study will examine the relative contribution of ACE and ACE2 activity to glomerular physiology and ANG peptides metabolism, and has the following aims: 1.To test the hypothesis that in isolated glomeruli from diabetic mice, ACE and ACE2 activity is altered such that ACE is increased and ACE2 is decreased, and this translates into corresponding alterations in ANG II formation and degradation to ANG (1-7). 2.To test the hypothesis that in isolated glomeruli from ACE and ACE2 knockout mice there is decreased ANG II formation and increased ANG II degradation, respectively, and that this is reflected in the levels of ANG II and ANG (1-7). 3. To test the hypothesis that the pattern of altered ACE and ACE2 activity in diabetic mice at the glomerular level has a functional counterpart we will measure albumin excretion, a marker of glomerular permeability, after ANG II infusion. We anticipate that in diabetic mice there will be an increase in albumin excretion which will correlate with glomerular, but not systemic ANG II. Nephropathy is a frequent complication of diabetes. Importantly, those diabetics who develop kidney complications have a much higher mortality than those who do not. The renin-angiotensin-system is a target of effective therapy for proteinuria and to delay kidney disease progression using ACE inhibitors and ANG II blockers. This proposal will provide a better understanding of ACE and ACE2 in diabetic kidney disease and has the promise to offer novel insights into ways to protect the kidney from diabetes related damage.